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Discussion Starter · #1 ·
Sadly, the bandit project I had underway has gone, so I am looking at refreshing my 1979 Moto Guzzi V50 Mk2. Yantosh is kindly helping out with a stem swap using some 1991 ZXR750 USD forks I am determined to use...axle will need sleeving which Yan is looking into so I can use the Guzzi front wheel as the ZXR one is wider than the stock Guzzi rear. Would have liked to use the ZXR front wheel but using anything other than the stock shaft drive for the Guzzi rules out any rear wheel swap of any significance.

Assuming it all goes together the Guzzi discs will not line up with the caliper. So, the long winded explanation leads me to asking if it is better to space out the discs from the wheel or space or make a new thick bracket for the ZXR brake caliper?
 

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is better to space out the discs from the wheel or space or make a new thick bracket for the ZXR brake caliper?
It’s really six of one/half a dozen of another IMO.
I do know that Ducati 748/996(8?)Rs used 15mm offset discs compared to the non-R’s 10mm offset. So there are a couple companies that sell a 5mm thick spacer for people swapping forks and wheels around. That being said on my Gpz project with a Zrx front end and a Ducati wheel I have 10mm offset rotors with a 5mm spacer AND still need a 3mm spacer between the caliper and fork mounts.

I guess it also depends on your level of fabrication and/or machining abilities. Some thick washers to space out the calipers will be a bunch easier than making a pair of identical rotor spacers. Of course, with Yan on your team it’s a mute point!

Later, Doug
 
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Discussion Starter · #5 ·
I dont have any fab/machining abilities above that of using a cutting disc and a hacksaw! i did make some rearset mounts for my abandoned bandit fighter which were okay. i wont know what i will have to do until i get the yokes back and can put it together...Yan is definitely a massive help...not sure i would get anywhere without his skills, help and knowledge.

i hadn't thought about making axle sized spacers to push the discs out...i was thinking that all the disc bolts would need a spacer each! but of course a single disc spacer each side makes sense. i just dont have the brain for this sort of thing. maybe a chunky ally caliper mount could also be considered.

thanks for the input guys...you have been a help already.
 

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One thing I just thought about with the rotor spacers is that they need to be really FLAT otherwise your rotor run-out will suffer. If you space out the calipers then the rotor run-out will be unaffected.

Are the rotor diameters the same?

Later, Doug
 
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One thing I just thought about with the rotor spacers is that they need to be really FLAT otherwise your rotor run-out will suffer. If you space out the calipers then the rotor run-out will be unaffected.

Are the rotor diameters the same?

Later, Doug
True. Even if machined out ideally they should be engineered to be surface ground
 

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I googled a pic of your bike. I think I got the right one. Your stock rotors have some serious offset built in to them.

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As they are not floating rotors you will have to be mindful to keep things flat for runout purposes, but OEM disc mounting surfaces aren't precision ground or anything drastic.

Also googled the ZXR750 front caliper. It's a rigid mount rather than floating on a carrier. That makes things easier for spacing the caliper. You might have to wait to see how the calipers interact with the spokes of your wheel. The Kawi calipers with the inboard pistons aren't very slim, so you'll need to keep an eye on clearances. That might dictate wether it's the disc or the caliper you have to move.
 

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Discussion Starter · #9 ·
that is my bike. there is a lot of offset on the discs which is why, from all your responses, i think making a caliper mount/spacers might be the way forward, but there is a lot to consider for sure. so it's not insurmountable and i appreciate possible solutions.
 

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Discussion Starter · #11 ·
another thought i had was, assuming i get everything lined up, would the 90's zxr calipers and m/c be too much for the bog basic 70's discs to cope with in terms of overheating and bits shearing off!?!
 

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I think the biggest problem will be the thickness of the rotor. Most sport-bikes are 5-6mm thick while older rotors can be much thicker. You’ll need to pay attention to the distance available between the pads. It may or may not be another issue.

Later, Doug
 
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